Purpose: Full recovery of atrial mechanical activity may not occur immediately after successful electrical cardioversion (ECV) of atrial fibrillation (AF) to sinus rhythm. Furthermore, timing of atrial contraction recovery is different among patients. This study was aimed to investigate predictive factor of early restoration of atrial mechanical activity after successful electrical cardioversion of atrial fibrillation to sinus rhythm. Method: Thirty-two consecutive patients (11 women, mean age= 64.2짹10.5) underwent successful ECV for nonvalvular long lasting persistent AF, and maintained sinus rhythm for 24 hours were enrolled to the study. To examine the atrial contraction recovery, serial two-dimentional, M-mode and transmitral pulsed Doppler echocardiogrpahic studies were performed before and after 24hours of ECV. Patients were divided into two groups according to E/A ratio of Pulsed Doppler echocardiography after 24hours of ECV: Group I (patients with E/A<1.5, n=12) and group II (patients with E/A>1.5, n=20). Results: The left atrial volume index by measured area-length method before ECV was lower in group I than in group II (25.8짹12.1 vs. 56.8짹 24.4, p=0.002). The left atrial volume index was correlated with E/A ratio after 24hours of ECV (p=0.039, r=0.367). Conclusion: This study results suggested that patients with small left atrium may have early restoration of atrial mechanical activity after successful electrical cardioversion (ECV) of long lasting persistent atrial fibrillation to sinus rhythm. Key Words: electrical cardioversion, persistent atrial fibrillation, atrial contraction.